A computer system, such as a stock trading system, in which stop of operation is not permitted, is referred to as mission critical. The computer system needs to be redundant to improve the reliability in a mission-critical computer system. Examples of techniques for making the system redundant include the following.
A first method is a method for making processes of applications redundant. The method is for replacing the processes so that the execution multiplicity of the processes becomes constant. In other words, two or more processes of an application are prepared, and a hot standby configuration is formed process by process. Specifically, two systems with the same configuration are prepared in the method, one system is set as a current system and operated, and the other system is set as a standby system and operated in the same way, while being set to a standby state. The standby system is always maintained in the same state with the current system, and when a failure occurs in the current system, the standby system quickly takes over the process.
A second method is a method for making the servers redundant. In the method, systems with the same configuration are prepared server by server, and a hot standby configuration is established.
There is known a communication system for communication between computers in which only the packets from specific processes can be preferentially processed in the terminals of a network system.
There is also known a remote control apparatus which can activate a lock knob when a new code is registered to display the registration of a new code signal.
There is also known a distributed shared memory calculation system which can realize the consistency guarantee control and the synchronous control with few network packets to effectively use the network resources, and can improve the performance to access the distributed shared memory.    Patent Document 1: Japanese Patent Laid-Open No. 4-180425    Patent Document 2: Japanese Patent Laid-Open No. 2001-227219    Patent Document 3: Japanese Patent Laid-Open No. 8-106440